Unusual Sb-Sb bonding in high temperature thermoelectric materials

The emerging families of advanced thermoelectrics are dominated by antimonides and tellurides. Becasue the structures of the tellurides are mostly composed of NaCl-related motifs, they do not contain any Te-Te bond, and all of the antimonide structures exhibit Sb-Sb bonds of various lengths. Taking all Sb-Sb distances shorter than 3.2 angstrom into account, the Sb atom substructures are Sb-2(4-) pairs in beta-Zn4Sb3, linear Sb-3(7-) units in Yb14MnSb11- planar Sb-4(4-) rectangles in the skutterudites, for example. LaFe3CoSb12, Sb-8 cubes interconnected via short Sb-Sb bonds to a three-dimensional network in Mo3Sb5Te2. These interactions have a significant impact on the band gap size as well as on the effective mass around the Fermi level, for the bottom of the conduction band is in all cases predominated by antibonding Sb-Sb interactions, and-in some cases-the top of the valence band by bonding Sb-Sb interactions. (C) 2008 Wiley Periodicals, Inc.